1. Field of the Invention
The present invention relates to control systems, and more particularly to a method and apparatus for synchronizing a motor's position and speed in a motor drive system.
2. Description of the Related Art
Many electrical and mechanical systems and environments include motor drive systems, which are energy conversion systems that produce mechanical/kinetic energy from electrical energy. The energy produced by motor drive systems is then used by various equipment units.
A typical motor drive system comprises a stator, a rotor, and a power inverter. The power inverter generates electromagnetic fields at the stator, which in turn cause the rotor to rotate. The position of the rotor during its movement is an important parameter used for control and monitoring of a motor drive system.
Hall effect sensors are typically placed inside a motor drive system and used to identify the rotor position in motor controls. Such Hall effect sensors are normally placed at 120 degrees apart for a three-phase motor, and are aligned with the back electromotive force (Emf) of the stator winding. Field Programmable Gate Arrays (FPGA) are typically used to count the duration of the rising edges between Hall effect signals, to compute the speed and angle of the rotor. This method of determining rotor motion parameters, however, is sensitive to noise, and hence is degraded by noise. When noises contaminate the rising edge of the Hall effect signals, the synchronization of the Hall effect signals to the back Emf of the motor drive system is lost, leading to the degradation of the motor drive performance. Motor controls failure can then occur.
Disclosed embodiments of this application address these and other issues by implementing a closed loop control that generates and locks motor reference signals to the fundamental component of the Hall effect signal generated by Hall effect devices. Even if a Hall effect signal is corrupted due to noise, the closed loop controls described in this application can automatically correct errors and maintain synchronization between Hall effect signals and motor reference signals. Disclosed embodiments of this application hence improve noise immunity of motor drive systems, by tracking to the fundamental components of the Hall effect signals. Even if the Hall effect signals are partially lost or corrupted, disclosed embodiments of this application continue to track and synchronize the motor drive reference signals with the fundamental frequency of the Hall effect signals.